Explanation:
How far away is "redshift six"?
Although humans are inherently familiar with
distance and
time,
what is actually measured for astronomical objects is
redshift,
a color displacement that depends on exactly how energy density has evolved in our universe.
Now since cosmological measurements in recent years have led to a
concordance on what
energy forms
pervade our universe, it is now possible to make a simple table relating observed
cosmological redshift, labeled "z", with standard concepts of distance and time, including the
extrapolated time
since the universe began.
One such table is
listed above, where redshift z is listed in the first and last columns,
while the corresponding universe age in billions of years is listed in the central column.
To find the meaning of the rest of the columns, please read the
accompanying technical paper.
Although stars in our galaxy are effectively at
cosmological redshift zero,
the most distant
supernovae
seen occur out
past redshift one,
which the above chart shows occurred when the universe was approximately half its present age.
By contrast, the most distant
gamma-ray bursts yet observed occur out
past redshift six, occurring when the universe was younger than one billion years old,
less than 10 percent of its present age.